1. Field of the Invention
The present invention relates to an in-line-three-beam-system color-cathode-ray-tube electron gun used for a color cathode-ray tube constituting a color picture tube or a color display unit and a color cathode-ray tube provided with the electron gun.
2. Description of the Related Art
A request for better resolution of a color cathode-ray tube is increasingly raised at present. Particularly, a problem of a spot shape of an electron beam around a screen is greatly focused on.
Moreover, a problem that preferable shapes of three electron beams cannot be obtained at the same time because a focus-voltage difference occurs between the three electron beams around a screen is particularly noticed.
This causes a generally observed phenomenon that a red character becomes unclear on the right side of a screen of a display monitor and a blue character becomes unclear at the left side of the screen.
To solve the above problem, a color-cathode-ray-tube electron gun having so-called built-in quadrupole lens is proposed.
FIG. 1 shows a schematic block diagram of a generally-widely-used, color-cathode-ray-tube electron gun having a built-in quadrupole lens.
The electron gun 70 has three cathodes KR, KG, and KB in-line-arranged in parallel, and a first electrode 11, a second electrode 12, a third electrode 13, a fourth electrode 14, a fifth electrode, a sixth electrode 16, and a shield cup 17 are coaxially arranged in order from the cathodes (KR, KG, and KB) toward an anode. Moreover, the fifth electrode is divided into a (5-1)th electrode 51 and a (5-2)th electrode 52. Furthermore, the second electrode 12 and the fourth electrode 14 are electrically connected to each other.
In the case of the color-cathode-ray-tube electron gun 70, a fixed-focus voltage (first focus voltage) Ef1 is applied to the third electrode 13 and the (5-1)th electrode 51 through a stem portion.
Moreover, a second focus voltage Ef2, on which a parabolic(so-called parabola-shaped)-waveform voltage horizontally-deflectively synchronizing with the first focus voltage Ef1 is superimposed, is applied to the (5-2)th electrode 52.
Thereby, a quadrupole lens (not illustrated) is formed between the (5-1)th electrode 51 and the (5-2)th electrode 52 and, moreover, the quadruole lens causes an intensity change in a focus lens (not illustrated) formed between the (5-2)th electrode 52 and the sixth electrode 16.
As a result, it is possible to form electron beams in the peripheral portions in the right and left directions of a fluorescent screen into preferable shapes.
FIG. 2 shows a schematic view of a color cathode-ray tube.
As shown in FIG. 2, three electron beams R, G, and B emitted from an electron gun 1 and colliding with circumferential portions of a fluorescent screen on the right and left sides are located away from each other in a magnetic field of a deflection yoke. Therefore, the directions and intensities of a magnetic field received by three electron beams are different from each other.
Therefore, the distortion states of electron beam spots at the right and left circumferential portions of the fluorescent screen 4 are different from each other among three electron beams R, G, and B. In FIG. 2, symbol 3 denotes a glass bulb. Moreover, xe2x80x9cRight Side of Screenxe2x80x9d and xe2x80x9cLeft Side of Screenxe2x80x9d denote the right side and the left side of the fluorescent screen 4 of the color cathode-ray tube when observing the screen 4 from the outside.
The focus voltage is usually set so that the shape of the spot of the central electron beam G among three electron beams R, G, and B becomes optimum.
In this case, when the three electron beams R, G, and B collide with the right side of the fluorescent screen 4, the red electron beam R passes through further outside of a deflection magnetic field formed by the deflection yoke 2 than the electron beams G and B and is greatly influenced by the deflection magnetic field. As a result, the distortion of the beam spot of the electron beam R on the fluorescent screen 4 becomes larger than those of the electron beams G and B.
Moreover, when the three electron beams R, G, and B collide with the left side of the fluorescent screen 4, the blue electron beam B passes through further outside of a deflection magnetic field formed by the deflection yoke 2 than the electron beams G and R and is greatly influenced by the deflection magnetic field. As a result, the distortion of the beam spot of the electron beam B on the fluorescent screen 4 becomes larger than those of the electron beams R and G.
Therefore, in the case of a display monitor, particularly a recent, large, color-display monitor having a high resolution, a phenomenon occurs that a red character becomes unclear at the right side of a screen and a blue character becomes unclear at the left side of the screen, as described above.
It can be said that the phenomenon occurs because a difference is produced around a screen among focus voltages of three electron beams R, G, and B.
Therefore, as one of the means for solving the problems, a color-cathode-ray-tube electron gun his been previously proposed which provides lens effects different in intensity for a red electron beam R and a blue electron beam B (refer to Japanese Patent Laid-Open Nos. Hei 11-067120 and Hei 11-149885).
FIG. 3 shows an electrode arrangement of a configuration of the above previously-proposed, color-cathode-ray-tube electron gun.
The electron gun 50 has three cathodes KR, KG, and KB in-line-arranged in parallel, and a first electrode 11, a second electrode 12, a third electrode 13, a fourth electrode 14, a fifth electrode (to be described later), a sixth electrode 16, and a shield cup 17 are coaxially arranged in order from the cathodes (KR, KG, and KB) toward an anode. Moreover, the second electrode 12 and the fourth electrode 14 are electrically connected to each other.
The fifth electrode corresponding to a focus electrode is divided into a (5-1)th electrode 51 and a (5-2)th electrode 52. Moreover, the (5-1)th electrode 51 is divided into a (5-1A)th electrode 51A, (5-1B)th electrode 51B, and a (5-1C)th electrode 51C.
A first quadrupole lens is constituted by the (5-1A)th electrode 51A, the (5-B)th electrode 51B, and the (5-1C)th electrode 51C, and a second quadrupole lens is constituted by the (5-1C)th electrode 51C and the (5-2)th electrode 52. Moreover, the quadruple-electrode action of the second quadrupole lens is controlled by the first quadrupole lens.
A fixed focus voltage (first focus voltage) Ef1 is applied to the third electrode 13 and the (5-1A)th electrode 51A and the (5-1C)th electrode 51C outside of the three-divided (5-1)th electrode 51. A third focus voltage Ef3 on which a voltage having a waveform voltage having a shape similar to serration synchronizing with horizontal deflection (refer to FIG. 4) and the fixed focus voltage Ef1 are superimposed is applied to the (5-1B)th electrode 51B. Moreover, a second focus voltage Ef2 on which a parabolic-waveform voltage synchronizing with horizontal deflection (refer to FIG. 4) and the fixed focus voltage Ef1 are superimposed is applied to the (5-2)th electrode 52.
These three focus voltages Ef1, Ef2, and Ef3 are normally supplied from a system portion at the front end of the electron gun 50.
A waveform of the third focus voltage Ef3 can be a waveform having a shape similar to the serration shown and linearly changing, as shown in FIG. 5A, or a sinusoidal waveform intermittently generated every horizontal deflection cycle, as shown in FIG. 5B.
The (5-1A)th electrode 51A, the (5-1)th electrode 51B, and the (5-1C)th electrode 51C are respectively provided with three electron-beam passing bores.
In the case of the above previously-proposed, color-cathode-ray-tube electron gun, it is possible to independently control deflection magnetic fields covering three electron beams R, G, and B by each electron beam by improving the shapes of the bores through which electron beams of the (5-1)th electrodes 51A, 51B, and 51C pass. By independently controlling the deflection magnetic fields, a difference between convergence effects of electron beams is canceled, preferable shapes of three electron beams are obtained around a screen, and the phenomenon that red is deteriorated on the right side of a screen and blue is deteriorated on the left side of the screen is eliminated.
In the case of the above method, however, its effect cannot be completely made the most of unless three types of focus voltages, that is, the fixed focus voltage Ef1, the parabolic-waveform voltage Ef2, and the serrated-waveform voltage Ef3 are independently adjusted. Therefore, adjustment is complex compared with the case of the conventional electron gun shown in FIG. 18 in which two types of focus voltages Ef1 and Ef2 only have to be adjusted.
Therefore, the present applicant proposes an electron gun having a constitution of applying the voltage obtained by passing the serrated-waveform voltage Ef3 through a built-in resistor to the (5-1A)th electrode 51A and the (5-1C)th electrode 51C instead of connecting the built-in resistor between the (5-1A)th electrode 51A and the (5-1C)th electrode 51C on one hand and the (5-1B)th electrode 51B on the other and applying the fixed focus voltage f1.
Thereby, the number of focus voltages to be adjusted is decreased to such two voltages as the parabolic-waveform voltage Ef2 and serrated-waveform voltage Ef3, and it is possible to avoid a complicated adjustment.
In the case of the method for supplying a voltage through a built-in resistor, however, a problem may occur that that electric potential is fluctuated due to crosstalk between electrodes and, thereby, a desired electric potential cannot be applied to an electrode differently from the case of directly applying a voltage to an electrode.
As a result, a quadrupole-lens action which should occur only at the right and left ends of a screen occurs at the center and the Y-axis ends (central upper and lower portions) of the screen, and, particularly, a phenomenon occurs that the focus characteristic at the Y-axis ends of the screen is deteriorated.
To solve the above problems, the present invention provides an in-line-three-beam-type, color-cathode-ray-tube electron gun and a color cathode-ray tube capable of reducing influences due to crosstalk between electrodes and uniforming spot shapes of three electron beams at the right and left ends of a fluorescent screen as much as possible.
A color-cathode-ray-tube electron gun of the present invention comprises a thrice-divided first focus electrode and a second focus electrode set so as to oppose the first focus electrode: wherein a parabolic-waveform voltage synchronizing with horizontal scanning is applied to the second focus electrode; of the thrice-divided focus electrodes, a built-in resistor electrically connecting the central electrode and both outside electrodes is provided, a voltage on which a first voltage component having a waveform similar to a serration and synchronizing with horizontal scanning, and a second voltage component having a parabolic waveform convex in the direction opposite to the parabolic waveform and synchronizing with horizontal scanning are superimposed is applied to the central electrode, and a voltage obtained by passing the voltage on which the first voltage component and second voltage component are superimposed through the built-in resistor is applied to both outside electrodes.
A color cathode-ray tube of the present invention is constituted by being equipped with the color-cathode-ray-tube electron gun having the above configuration.
According to the color-cathode-ray-tube electron gun and color cathode-ray tube of the present invention, because the voltage obtained by passing the voltage on which the first voltage component and second voltage component are superimposed through the built-in resistor is applied to both outside electrodes of the first focus electrode, a component obtained by passing the second voltage component convex in the opposite direction to the parabolic waveform of the voltage to be applied to the second focus electrode is applied to the both outside electrodes. The component makes it possible to offset the influences of crosstalk from the second focus electrode to which a parabolic-waveform voltage is applied to both outside electrodes.